If you have no wireless router then don't bother buying the wireless kit for the Xbox, it will be a waste of money.
I'm assuming you have a wired router at the moment. If so, you'll need to mess around with that to get it to allocate an IP to your 360. If you're running an Ethernet cable from the back to the Ethernet port on your computer then you'll need to mess around to sort the network connections out.
Not the most techy answer going, I'm sure someone else will do a lot better